A nurse is taking a health history of a client who reports occasionally taking several over-the-counter medications, including an H2 receptor antagonist (famotidine). Which of the following outcomes indicates that famotidine is therapeutic?

The correct answer is A: Relief of heartburn. Famotidine is an H2 receptor antagonist used to reduce stomach acid production, providing relief from symptoms such as heartburn. This outcome indicates that famotidine is working as intended by reducing acid levels in the stomach, leading to relief of heartburn. Choices B, C, and D are incorrect as they do not directly relate to the mechanism of action of famotidine. Cessation of diarrhea, passage of flatus, and absence of constipation are not typically associated with the use of an H2 receptor antagonist like famotidine. Therefore, the relief of heartburn is the most appropriate outcome to indicate that famotidine is therapeutic in this scenario.